Impurities may become entrained in a gas stream as a result of certain industrial operations. These impurities could be broadly termed volatile organic compounds ("VOC"). Since the gas, such as air, used in the industrial operation may have to be recycled or exhausted to atmosphere, it becomes important to remove VOC from the gas. There are strict regulations that mandate maximum VOC levels in air which is exhausted from industrial exhaust stacks. The pollution equipment for combusting, and hence removing, VOC has become quite sophisticated over the past several years. Every feature of the equipment design is optimized to reduce power usage, and increase cleaning efficiency.
A regenerative incinerator of the type addressed in this patent application can generally be defined as a system which maximizes VOC destruction at the lowest possible cost in terms of energy requirements. This is achieved by integrating three fundamental steps: a VOC-laden gas stream is preheated to a temperature near its combustion point; the VOCs are oxidized by a combustion flame; and heat is removed from the hot purified gases in which the VOCs have been oxidized, and used to preheat subsequent incoming VOC-laden gases. This basic process has proven to be an efficient method of VOC destruction.
A number of regenerative incinerators are known which utilize this basic process for VOC destruction. These systems are generally characterized by a plurality of heat exchangers connected to a common combustion chamber, in which a gas burner is positioned. Each heat exchange chamber includes at least one port through which a gas stream flows during operation. In addition, each heat exchange chamber is packed with a heat exchange material which serve to transfer heat between cool, incoming gases to be cleaned and hot, outgoing cleaned gases.
In a typical operation, VOC-laden gases are directed into a first heat exchange chamber such that they flow through the chamber in contact with the heat exchange material and toward the common combustion chamber. In the common combustion chamber the VOCs are oxidized by the flame from the gas burner. After combustion, the purified gas stream contains a substantial amount of heat energy which would be lost if the purified gases were simply vented to atmosphere. Instead, the heat is regenerated by flowing the hot, cleaned gases through a second heat exchanger. The hot gases heat the heat exchange materials in the second heat exchanger. After the heat exchange material has been heated in this manner, the flow of incoming VOC-laden gases is redirected such that it moves through the heat exchange material in the second heat exchanger, and to the combustion chamber. Valving systems control the alternate flow of the gases through the heat exchangers. In this manner, the incoming gases are preheated.
Commercial systems of this type process extremely large volumes of gases. The individual heat exchangers may process a volume from about 7,000 to several hundred thousand cubic feet per minute. In order to preheat the large volume of gas (and to extract heat from the gas) a corresponding volume of heat exchange material is needed to pack the chambers. In a typical regenerative incinerator, the heat exchange material in a single heat exchanger may have a mass in excess of 65,000 pounds.
In conventional regenerative incinerators, the heat exchange material is supported in each chamber by a grate which defines a region of space beneath it. Gases flow between the space and the combustion chamber through the heat exchange material. This allows for relatively even flow and distribution of the gases through the heat exchange material and prevents any obstruction of the inlet/outlet port by the heat exchange material.
This method of supporting heat exchange material on a grate has one important drawback. Due to the massive weight of the heat exchange material, the grate may sag and/or detach from the side walls of the heat exchange chambers. This allows the heat exchange material to flow downwardly into the bottom of the heat exchanger, and interfere with the flow of gases through the port and with the even distribution of gases through the heat exchanger. The catastrophic failure of a grate results in downtime as well as considerable expense in association with the removal of the heat exchange material and repair of the grate. Thus, there exists a need for an alternative to the conventional grate supported heat exchange material in heat exchangers of regenerative incinerators. The present invention achieves this goal.